In recent years, in broadband wireless communication systems, OFDMA that assigns different terminal apparatuses to respective parts of the system band has been attracting attention. OFDMA is a multi dimensional access technology based on OFDM in which subcarriers perpendicular to each other are arranged on a frequency axis, and a segment in which a plurality of subcarriers are bundled up is set as a resource unit, and a base station apparatus assigns different segments to respective terminal apparatuses.
To increase the frequency usage efficiency of the wireless communication system using OFDMA, it is effective to compare the communication quality of every segment in each terminal apparatus so as to assign each segment to the terminal apparatus having a preferable quality. In the wireless communication system, communication quality changes with time. Accordingly, in the case of downlink communications, each terminal apparatus measures the communication quality at a specified spacing, and feeds it back to the base station apparatus. The technology to dynamically assign the frequency segment whose communication quality is preferable to each terminal apparatus is called a frequency scheduling technology, and it has been studied flourishingly (for example, refer to Patent Document 1 or Non-Patent Document 1).
As the representative algorithms of the scheduling, there are known three kinds that are: (1) Maximum CIR Algorithm; (2) Round Robin Algorithm; and (3) Proportional Fairness Algorithm. In the algorithm (1), transmission opportunities are assigned with priority to a terminal apparatus whose communication quality is preferable. As the communication opportunities with the terminal apparatuses near the base station apparatus increase, communication opportunities with the terminal apparatuses at distant places decrease; therefore, it is a scheduling algorithm in which the service differences become large among the terminal apparatuses. In the algorithm (2), the communication opportunities are assigned to all terminal apparatuses equally. In comparison with (1), as the communication opportunities with the terminal apparatuses at the distant place are increased, the throughput of the base station apparatus is declined. In the algorithm (3), a value of (real-time communication quality)/(average communication quality) is used as the evaluation value, and the transmission opportunities are assigned with priority to the terminal apparatus whose evaluation value is large, and accordingly, it is an algorithm in which the communication opportunities are equal, and the frequency usage efficiency is superior to (2). However, it is a problem that the base station apparatus must precisely know the real-time downlink communication quality in every wireless terminal apparatus.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2002-252619
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2005-244958
Non-Patent Document 1: “MC-CDM System for Packet Communications Using Frequency Scheduling”, IEICE Technical Report, RCS2002-129, Jul., 2002, p. 61-66
Non-Patent Document 2: 3GPP2 C.S0024-A “cdma2000 High Rate Packet Data Air Interface Specification” (page 11-80, Mar. 31, 2004)
Non-Patent Document 3: 3GPP TR 25.814 V1.1.1, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Layer Aspects for Evolved UTRA (Release7)” (pages 18 and 24, 2006/2)
Non-Patent Document 4: Jim Tomcik, “QFDD and QTDD: Technology Overview”, Contributions on IEEE 802.20 Mobile Broadband Wireless Access, IEEE C802.20-05/68r1, Jan. 2006. (pages 79 to 84)